228 BEHAVIOR OF THE LOWER ORGANISMS 



this was not due to any actual inability of the centre to initiate move- 

 ment, for Romanes found that when it was stimulated in various ways, 

 it contracts rhythmically. This occurred in the centre of the bell of 

 Sarsia when placed in certain chemicals, notably in weak acids, and 

 in a glycerine solution (Romanes, 1885, pp. 190-197). Rhythmical 

 contractions have likewise been observed by Loeb (1900 a) in the iso- 

 lated centre of Gonionemus when placed in a pure solution of sodium 

 chloride. Thus it is clear that not only the margin, containing the 

 greater part of the nervous system, but also the centre of the bell, has 

 the power of contracting rhythmically. 



These and many other experiments have shown that each part of 

 the body has in the ccelenterates certain characteristic ways of reacting 

 to stimuli, and that it may react in these ways even when separated 

 from the rest of the body. Its reactions may be determined within 

 itself. But from this the conclusion cannot be drawn that the behavior 

 of these animals consists entirely of the separate and independent re- 

 actions of these parts to external stimuli. While each part may react 

 independently, each may also react with reference to influences coming 

 from other parts of the body. Thus, the tentacles may react, not only 

 to external stimuli directly impinging upon them, but also, in many 

 coelenterates at least, to stimuli that are transmitted from other parts. 

 A strong stimulus on the body or on a single tentacle causes a contrac- 

 tion of many tentacles. In some cases this contraction of the other 

 tentacles appears to be due to a direct spreading of the muscular con- 

 traction. One fibre pulls on another, setting it in action, until the pull 

 reaches the base of the tentacle. This pull then acts as a direct stimu- 

 lus, causing the tentacle to contract, in the same way that would occur 

 if it were mechanically stimulated from outside. This is the way in 

 which Torrey conceives of the matter in Sagartia. If this is the correct 

 explanation, there is of course nothing comparable to nervous trans- 

 mission passage of a wave of stimulation independently of a wave of 

 contraction in these cases. 



In Aiptasia annulata, on the other hand, a light stimulus on the tip 

 of one of the long tentacles induces a sudden quick contraction of the 

 entire body. This contraction appears to the eye to take place over 

 the entire body at once, and it is so rapid as to suggest strongly the opera- 

 tion of a conducting nervous system. The w T ell-known experiments of 

 Romanes (1885, p. 76) demonstrated completely that in medusae there 

 is such a wave of stimulation independent of a wave of contraction, 

 and that this wave of stimulation coming from other parts of the body 

 causes the tentacles to contract. By cutting off the margin of Aurelia 

 in the form of a long strip and stimulating one end, he could cause a 



